Resolve inconsistency with tensor strides and optimizer updates

[ferrine]

Adress #70

[NProkoptsev]

It seems copy_() takes more time than set_(), this will be more prominent if most of parameters will be without manifold constraints
You can check if tensors properties match each other

if point.stride() != new_point.stride():
    point.copy_(new_point)
else:
    point.set_(new_point)

[SomeoneSerge]

Just by the way... If I were doing it, I'd want to provide an explicit hint that one of the arguments is Tensor & and not const Tensor &, so perhaps a _ at the end: copy_or_set_().

is still awaiting for review

Well, really not the part that needed review

[ferrine]

@newkozlukov, thanks, that is a better name for this. I skimmed over the codebase, looks like all critical places are covered with this function

[ferrine]

Thanks all